To BMS or not...

Power wheelchair board for REAL info!

POWERCHAIR MENU! www.wheelchairdriver.com/powerchair-stuff.htm

Re: To BMS or not...

Postby Burgerman » 13 Nov 2020, 13:25

You can't set it to 4 digits in normal mode BM.
Steve


Shirley can I think.
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby shirley_hkg » 13 Nov 2020, 14:58

This is the log and following 4 hours .

No. I can't have 4 decimal neither.
Attachments
ChineseChinese Graph.CP8.zip
(105.66 KiB) Downloaded 157 times
Screen 00128.jpg
shirley_hkg
 
Posts: 3045
Joined: 31 Dec 2010, 13:42

Re: To BMS or not...

Postby Burgerman » 13 Nov 2020, 16:27

Check PM

Setting 4 decimal figures also removes all data rounding. Shows absolute voltages. Average user doesent want that. You might.
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby shirley_hkg » 14 Nov 2020, 09:36

Fully discharged and re-charged. During daily use, it took 10 mins to balance ; quite similar to PL8.

This is the usable BMS I met so far , for large Ah battery.

I will still use PL8, but can be an alternative to it.
Attachments
Screen 00130.jpg
shirley_hkg
 
Posts: 3045
Joined: 31 Dec 2010, 13:42

Re: To BMS or not...

Postby Burgerman » 14 Nov 2020, 11:10

Why does it have that huge dip?
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby terry2 » 14 Nov 2020, 11:39

shirley_hkg wrote: Fully discharged and re-charged. During daily use, it took 10 mins to balance ; quite similar to PL8.

This is the usable BMS I met so far , for large Ah battery.

I will still use PL8, but can be an alternative to it.



That looks fantastic :)

Will the app be in english?
If so how much?

Thanks
User avatar
terry2
 
Posts: 1209
Joined: 07 Nov 2014, 12:08
Location: Solihull

Re: To BMS or not...

Postby shirley_hkg » 14 Nov 2020, 13:49

Burgerman wrote:Why does it have that huge dip?


It's because the set charge volt is reached. Charger disconnected. Equalization in process . Low cells are fed by high cells .

Balance completed with ONE cycle. That's nice.

About English menu , it doesn't exist . Never mind . You don't need it. It has only (TWO) parameters to set.
shirley_hkg
 
Posts: 3045
Joined: 31 Dec 2010, 13:42

Re: To BMS or not...

Postby Burgerman » 14 Nov 2020, 13:55

But its not supposed to stop when charge voltage is reached. It shoud sit at CV to allow the cells to become full, or the reached voltage will be false due to cell and cable resistance and speed of charge acceptance.. So it should continue until say 300thC after balance is complete.

Set to 4 cell next tim using .reg files. Then we can see what it really does!
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby shirley_hkg » 14 Nov 2020, 16:42


Can we tell how fully the battery is charged, by looking at the volts of the following hours ?


May leave it to undergo more balance cycles for soaking further .
Attachments
Screen 00128.jpg
shirley_hkg
 
Posts: 3045
Joined: 31 Dec 2010, 13:42

Re: To BMS or not...

Postby steves1977uk » 14 Nov 2020, 17:56

Can't you set a termination current on that BMS Shirley?, E.g. For a healthy 100Ah pack it should terminate at 100mA, or higher if cells have been used a lot.

Steve
User avatar
steves1977uk
 
Posts: 3407
Joined: 20 Oct 2011, 21:47
Location: Wells next the Sea, Norfolk, UK

Re: To BMS or not...

Postby Burgerman » 14 Nov 2020, 21:55

Its a BMS and cant control the charger so it cant do that. In order to balance, and not send the voltage sky high it can only disconnect the power supply/charger or whatever. The balance happens all the time above x volts. But the charger can only be kicked off and reconnected. Hence the strange looking graph. Every time its reconnected it goes overvolt and has to be disconnected. So a low current cannot be done. Just rinse and repeat with too much voltage.. Thats why I say that a BMS is in the wrong place. It needs to be able to control the charger output so that chage current can be less than the balance current. And less than it needs to maintain a steady 3.600V without overvolting over and over. So even this one has the same issues.

Can we tell how fully the battery is charged, by looking at the volts of the following hours ?


No.
We need to apply a voltage above 3.5V preferably 3.55 to 3.60V and then watch the charge current decay over time. And after balance has ended. Then we know its charged. Otherwise, we dont. And balancing as you are doing below 3.5V will not balance at all or very badly. It mayeven unbalance othwerwise balanced cells.
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby snaker » 15 Nov 2020, 03:54

Shirley, what was the current that you set to charge the pack? Is it adjustable through app? What are its min/max values?
User avatar
snaker
 
Posts: 1017
Joined: 23 May 2015, 10:45
Location: Vietnam

Re: To BMS or not...

Postby shirley_hkg » 15 Nov 2020, 08:15

NO.
It depends on the charger.
shirley_hkg
 
Posts: 3045
Joined: 31 Dec 2010, 13:42

Re: To BMS or not...

Postby Burgerman » 15 Nov 2020, 09:33

What he means is that if you use a power supply it will keep bouncing on and off forever. And if its a wheelchair charger it will think that you reached a fully charged start because a osfet disconnects it and the charger turns off or goes to a float voltage. Or whatever each charger does.

So you would have to keep on restarting the charger. As I said, BMS :thumbdown: Its in the wrong place.

As it is those cells are not full. May not be balanced because voltage too low.
Try using 4 digits, charge to 3.600V.
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby shirley_hkg » 15 Nov 2020, 12:00

Burgerman wrote:Every time its reconnected it goes overvolt and has to be disconnected. So a low current cannot be done. Just rinse and repeat with too much voltage.



I didn't see it over-volted. Even if it did, it wouldn't do much harm, as it was only superficial when PL8 couldn't see it at all.



No.
We need to apply a voltage above 3.5V preferably 3.55 to 3.60V and then watch the charge current decay over time. And after balance has ended. Then we know its charged. Otherwise, we dont. And balancing as you are doing below 3.5V will not balance at all or very badly. It mayeven unbalance othwerwise balanced cells.


It's 99% charged @3.45V. I seldom charge up to 3.6V , and have been balancing @ 3.4V.






I'm not optimistic about the reproduction of PL8, so I need plan B .
shirley_hkg
 
Posts: 3045
Joined: 31 Dec 2010, 13:42

Re: To BMS or not...

Postby Burgerman » 15 Nov 2020, 12:21

It's 99% charged @3.45V. I seldom charge up to 3.6V , and have been balancing @ 3.4V.

You cannot correctly balance at 3.4V. Or 3.45V unless you hold it at 3.45 for at least 3 or 4 hours. Because little current flows and its near resting voltage. Even if charged at a very low current.

Also you cant stop charging just because it reached any particular voltage.
If I charge at 40 or 50A then I see that 4.5V much sooner due to internal resistances. A far more full charge would be achieved at 1A charge.

When I stop charge at 3.45V its far from charged or balanced if charging at a high rate. You must allow the current to drop from the 40, 30, or 20A till its at almost zero. Thats the only way to ensure a good balannce and a known state of charge.
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby Tomkilmore » 16 Nov 2020, 23:40

Shirley...why not use 2x PL6 as a backup?
Tomkilmore
 
Posts: 331
Joined: 27 Sep 2010, 14:05
Location: beckingham. doncaster

Re: To BMS or not...

Postby shirley_hkg » 24 Nov 2020, 08:04


Thanks PL8's monitoring. We can see high cells , by feeding the low cells, are no longer being held at high voltage during balancing .
Attachments
Screen 00127.jpg
shirley_hkg
 
Posts: 3045
Joined: 31 Dec 2010, 13:42

Re: To BMS or not...

Postby Burgerman » 24 Nov 2020, 09:38

Those are not balanced.
You need to be above 3.5V at the end to balance LiFePO4 cells.
And you must use 4 digits! Or the balance is averaged.
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby shirley_hkg » 24 Nov 2020, 12:11

shirley_hkg wrote:

The battery :

It's a 70Ah pouch cells , with loose, messy connections.
It's pre-balanced by PL8 , and is removed 60Ah out of it , and it is also deliberately unbalanced by taken 3 to 5 Ah amongst cells 3 to 8 as well.

It is in every way an out of balance pack now .


It was a demo , John .

Will you still want the pack that it could be 5ah out of balance in every cycle use ?


Immediate recharge showed that balance completed in minutes , so it could be set to ≥ 3.5V .

I'm installing it , while PL8 is still impossible .

By the way, are you optimistic about PL8's coming back again , and why ? cheers drunk2

shirley_hkg
 
Posts: 3045
Joined: 31 Dec 2010, 13:42

Re: To BMS or not...

Postby Burgerman » 24 Nov 2020, 13:01

Yes, because its the best charger thay have by far. But not the most popular. Most people want dumb stuff. And because its common for hobby stuff to be out of stock over winter. And we have corona problems and so cashflow issues....

It was a demo , John .

Will you still want the pack that it could be 5ah out of balance in every cycle use ?
Immediate recharge showed that balance completed in minutes , so it could be set to ≥ 3.5V .


Set it to 3.600V and watch. If it shows balanced at 3.600V without overvolting or bouncing, and with 4 decimal places (averaging removed) then its balanced... It could be 10Ah out of balance or more right now because you cannot balance below 3.5V - thats where balance should start.
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby shirley_hkg » 29 Nov 2020, 05:27


Made a D_sub connector for real application.

Gonna charge my chair's 300Ah pack , which has bad connection issues, as I noted via PL8.

See if it will ease BM's concern a bit .
Attachments
IMG-20201129-WA0004.jpg
shirley_hkg
 
Posts: 3045
Joined: 31 Dec 2010, 13:42

Re: To BMS or not...

Postby Burgerman » 29 Nov 2020, 13:56

Not really! Its doing it wrong!
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby shirley_hkg » 29 Nov 2020, 16:00

cheers drunk2
Attachments
Screen 00039.jpg
shirley_hkg
 
Posts: 3045
Joined: 31 Dec 2010, 13:42

Re: To BMS or not...

Postby Burgerman » 29 Nov 2020, 16:38

Thats terrible.
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby shirley_hkg » 30 Nov 2020, 00:30


Sort of. Doesn't look much prettier on PL8 due to bad connections in the battery.

ZXD @28.8V/20A
BMS @3.6V & balance starts @3.4V.

Never cross 3.6V , and will end with one solid line , like previous pic.

Need to go , so couldn't wait till it ended .
shirley_hkg
 
Posts: 3045
Joined: 31 Dec 2010, 13:42

Re: To BMS or not...

Postby Burgerman » 30 Nov 2020, 00:39

Balance should never start at 3.4v though. You can unbalance a pack by attempting to balance at 3.4v.
3.5v is the lowest level. And it must happen at 3.5 not while bouncing up and down!
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby steves1977uk » 30 Nov 2020, 15:31

Bouncing is fun though BM!! :mrgreen: Especially with women. ;)

Steve
User avatar
steves1977uk
 
Posts: 3407
Joined: 20 Oct 2011, 21:47
Location: Wells next the Sea, Norfolk, UK

Re: To BMS or not...

Postby Burgerman » 30 Nov 2020, 17:33

I gave all that up. Mostly. When I became T4 paraplegic... Although did find a couple that wanted to try! But I have decided that women are all too much trouble now at 60. I became a hermit! ;)
User avatar
Burgerman
Site Admin
 
Posts: 54806
Joined: 27 May 2008, 21:24
Location: United Kingdom

Re: To BMS or not...

Postby snaker » 02 Dec 2020, 03:47

Burgerman wrote:Balance should never start at 3.4v though. You can unbalance a pack by attempting to balance at 3.4v.
3.5v is the lowest level. And it must happen at 3.5 not while bouncing up and down!


This BMS balances cells by taking the highest cell to charge the lower cells. After the BMS cuts off charging, all cell volts drop under 3.500v or even 3.450v. I think that's why Shirley set the balance starting voltage to a low value 3.400v.

@Shirley: why not set it a bit higher e.g 3.425v or 3.450v and see what happens? Does this BMS manufacturer release docs in English or Chinese? So we can write an app to directly monitor cell volts in graphs without needing PL8.
User avatar
snaker
 
Posts: 1017
Joined: 23 May 2015, 10:45
Location: Vietnam

PreviousNext

Return to Everything Powerchair

Who is online

Users browsing this forum: Bubbernator, Burgerman, Darrell_LeRoy, Google [Bot], hobie1dog, LROBBINS, rickystyx, woodygb and 42 guests

 

  eXTReMe Tracker